Tomatoes in Florida and elsewhere are often picked green and then transported and stored at low temperatures to extend their shelf life before they make it to store shelves.

Jinhe Bai, an Agricultural Research Service chemist at the U.S. Horticultural Research Laboratory in Fort Pierce, Florida, wondered if chilling causes tomatoes to lose their flavor and whether it’s why “supermarket tomatoes” often taste so bland. The chilling slows ripening, but like many other tropical and subtropical crops, tomatoes are sensitive to low temperatures. In some fruits, chilling is known to cause internal “chilling injuries,” Bai says.

Bai and his colleagues harvested 120 standard “Florida 47” variety tomatoes at the “mature green” stage and subjected 30 tomatoes each to 1 of 4 treatments: applying heat only; chilling (to the industry standard of 41 ˚F); heating prior to chilling; and keeping them at room temperature (controls). In the heat treatment, the tomatoes were kept heated at 125 ˚F in hot water for 5 minutes. Like commercially produced tomatoes, tomatoes in the study were ripened at 68 ˚F after being exposed to the temperature treatments.

Samples of each group were cut and placed into sealed containers. The containers were opened less than an hour later, and the tomatoes were rated for flavor by 21 volunteers, based on the aromas released. The study was designed to evaluate fruit aroma, so only the odors were assessed to eliminate any bias from taste and “mouth feel,” said Anne Plotto, the ARS scientist who supervised that part of the study. The researchers also used gas chromatography-mass spectrometry to identify levels of 12 key volatile aroma compounds known to give tomatoes their flavor.

The results show that applying a heat treatment to mature green tomatoes before they are chilled and shipped improves their flavor. Specifically, heating the tomatoes before chilling stemmed the loss of several flavor volatiles, including two key carotenoid-derived aroma compounds that give fruity and floral scents to foods as diverse as citrus and saffron. The heated-then-chilled tomatoes also had more flavor volatiles than the tomatoes that were only chilled: 14 out of 21 panelists could detect that they had more tomato aroma.

Applying heat alone to the tomatoes did not affect levels of volatiles once those tomatoes had ripened. “Just heating tomatoes doesn’t seem to help,” Bai says. However, heating and then chilling increases the tomato’s resistance to the internal chilling injury that is causing the loss of the aroma compounds, Bai says.

Unfortunately, it doesn’t help to heat and chill a ripe tomato purchased off a store shelf, he says. Previous research has shown that once tomatoes have ripened, heating or chilling them can suppress flavor volatiles beyond repair. For maximum effect, the heating and chilling process should be applied when the tomatoes are still green, but it also will benefit tomatoes at the “breaker stage,” the point when they first begin to turn red.

The results should help tomato producers and packers address consumer complaints about flavorless fruit. They can apply the heat by just immersing tomatoes in 125 ˚F water for 5 minutes, Bai says. He is working with packers to make sure they know about the technique. “There’s no negative effect from the hot water treatment and it will help to kill fungi or bacteria on the surface of the fruit that cause postharvest diseases, and it should be an easy practice to adopt,” he says.—By Dennis O’Brien, Agricultural Research Service Information Staff.

"Recipe for Flavorful Tomatoes" was published in the May 2015 issue of AgResearch Magazine.

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